Imagine biting into a piece of cake with a thick layer of frosting at the bottom instead of at the top. Robin Bell and here team of scientists have found a similar scenario in at the bottom of Antarctic ice sheets, where freezing water is responsible for as much as half of the ice sheet’s thickness. The findings, she says, indicate that water moving through ancient river valleys beneath more than one mile of ice has changed the basic structure of ice sheets.

“We went to the middle of the ice sheet to explore the hidden mountain ranges,” Bell told WINGS, adding that, “usually the ice sheet looks like a nice pile of tortillas. Finding the frozen ice was like discovering a dollop of guacamole under the ice sheet. At first we thought is was an error but there the features were again and again.”

Fully equipped Twin Otter on skis taking off from AGAP-S camp at 3500m heading north to survey over Dome A. Four radar antennae can be seen hanging down on each wing. Energy was transmitted from the four antenna on the left wing, through the ice sheet where it reflected off layers in the ice and the hidden mountains. The returning energy was received on the four antennae on the right wing. The pods on the ends of the wings contain the magnetometers. The gravity meter and the laser altimeter are mounting inside the aircraft. [Nick Frearson--Lamont Doherty Earth Observatory, New York]The study was part of a collaborative effort of seven countries to study one of the most remote parts of Antarctica, known as “Dome A.” The 4,200-meter Dome A—an area the size of California—is the top of the East Antarctic ice sheet. Large ice sheets like the one that covers Antarctica grow when falling snow accumulates faster than it disappears, over long periods of time, causing thickening and lateral spreading. But it turns out that this type of accumulation is not the only way that these ice sheets can thicken. Using state-of-the-art ice imaging systems, Bell and colleagues discovered that a large fraction of the ice at Dome A accumulated by the freezing of water at the bottom of the ice sheet, rather than from snowfall onto surface of the ice sheet. This process occurs when water pooled at the bottom of the ice sheet is cooled by convection, or when water forced up steep valley walls is super-cooled; altering the thermal and crystal structures of the ice column as well as the topography of the ice sheet surface.

AGAP south camp on East Antarctic Plateau resting atop over 2 kilometers of ice. On the south side of Dome A at 3500m above sea level, this camp was one of two camps that supported the scientists studying the Gamburtsev Mountains and the overlying ice sheet. [Robin E. Bell--Lamont Doherty Earth Observatory, New York]

Although water has long been known to be important to ice sheet dynamics (mostly as a lubricant), Bell’s study reveals just how drastically

basal water can modify the structure of ice sheets. Scientists need to understand how ice sheets are put together in order to accurately predict how they will be affected by global climate change.

Ice penetrating radar over the freeze-on ice along the southern margin of the Gamburtsev Mountains. The plume of freeze-on ice is 1100m thick along this profile and the normally flat internal layers are deflected upward 400m. [Robin E. Bell--Lamont Doherty Earth Observatory, New York]

Related Links and information:

Bell and her team have published the results of their study in the 03 March 2011online edition of Science magazine. http://www.sciencexpress.org.